Gas turbine engines include numerous bearings, many of them operating at high speed, that require continuous lubrication to preserve the integrity of the engine. Under normal operating conditions, the bearings receive lubrication from the engine's oil supply system. However, if that supply of oil is interrupted, whether due to faulty operation or damage from enemy action as in military aircraft, the bearings would fail almost immediately for lack of lubrication with disastrous consequences. To cope with such situations, it is imperative that an emergency backup system be provided so that the engine can continue to operate safely for a time sufficient to permit its operator to shut down the engine and take steps to protect his own safety.
The invention of our prior U.S. Pat. No. 4,717,000 comprises an integrated emergency lubrication system that provides continuous lubrication for the bearings of a gas turbine engine assuring safe operation at nearly full power for several minutes in the event the engine's main oil supply fails. The emergency system is highly reliable, easily maintained, and relative invulnerable to damage yet can be manufactured at relatively low cost.
However we have found that the emergency lubrication system of said Patent is more complex than is necessary, with resultant additional weight and expense.
In the system of U.S. Pat. No. 4,717,000, the emergency oil supply is forced by regulated, reduced air pressure to the individual bearing sump and gearbox nozzles through an oil supply line to each nozzle, while the regulated air is fed to the individual nozzles through a separate air supply line to each nozzle. The oil and air are mixed and misted at each nozzle, requiring separate oil and air lines to each gearbox. This increases the weight and cost of the system as well as the possibility of failure due to the number of components.
Also, in the system of U.S. Pat. No. 4,717,000, the oil pressure in the accumulator during emergency operation is the same as the regulated air pressure to the nozzles. This means that the oil flow from the accumulator is dependent upon the regulated air pressure and the downstream conduits and orifices, and is sensitive to oil temperatures and variations in the pressure drop of the system. Thus the rate of oil flow from the accumulator during emergency operation is variable and cannot be assured to last for a predetermined desired period of time, i.e., about six minutes for an accumulator oil capacity of about 500 cc.